The proposed study investigates the quantitative distribution of retinol and retinyl esters in blood and liver cell types (hepatocytes and Kupffer cells) and in subcellular organelles when dietary conditions are such as to favor mobilization, a steady state or deposition at three levels of dietary vitamin A (low, moderate, high). Presently there is no entirely satisfactory means of evaluating intermediate levels of vitamin A in blood since these do not necessarily parallel the levels in tissue stores. Nor is there a clear understanding of the relative physiological meaning of a moderate or high liver reserve. This dilemma is due, in part, to an inadequate understanding of factors which regulate the mobilization of vitamin A from storage tissue. Clearly the availability of transport protein is essential, but equally important prior to binding is the release of retinol from its usual storage form as an ester with fatty acid. The sequence of events and enzymes involved in the hydrolysis and the hepatic secretion of vitamin A are not defined. Also lacking confirmation is the specific cell types in the liver in which these events occur and the subcellular location of hydrolytic enzyme and substrate. Differential enzyme digestion, ultracentrifugation, gas chromatographic and radioisotope techniques are used in the proposed study to investigate the distribution of retinol and its ester in different cell types and subcellular organelles during mobilization, steady state and deposition from and into hepatic tissue.